As the nitrosochlorides of different terpenes show very similar melting points and besides decompose very readily, they are less suitable for characterization than the nitrolamines, which are very stable and crystallize readily; these have been prepared in large numbers, although the compounds produced by the reaction with benzylamine and piperidine are preferably used. For their preparation4) the nitrosochloride is treated in excess with the base dissolved in alcohol and heated on a water bath; the nitrolamine formed is separated by the addition of water. The melting point of pinene nitrolpiperidine is 118 to 119°, that of the nitrolbenzylamine 122 to 123°.
It has already been pointed out that the yield of nitroso-chloride diminishes with the increased optical rotation of the hydrocarbon material.5) For the identification of pinene in highly active pinene fractions it is, therefore, more expedient to make use of the pinonic acid referred to above. 100 g. of pinene are shaken with 233 g. of potassium permanganate and 3 1. of water, the mixture being kept cool with ice. From the alkaline reaction mixture the excess of hydrocarbon is separated and the neutral products are removed by shaking with ether. The pinonic acid is then precipitated with dilute sulphuric acid. For the identification of the pinene it suffices to convert the acid into its semicarbazone (m. p. 204°). If it is desired to establish the presence of optically active as well as inactive pinene, it is necessary to isolate the acid in its pure form. In most instances this can be accomplished by fractionation under diminished pressure (b. p. 168° at 12 mm.). The identification is com- pleted by determining the angle of rotation and by preparing the derivatives of the acid already described.
1) Bed. Berichte 29 (1896), 12.
2) Wallach and Lorentz, Liebig's Annalen 268 (1891), 198.
3) Urban and Kremers, Am. Chem. Journ. 16 (1894), 404; Baeyer, Bed. Berichte 28 (1895), 646; Mead and Kremers, Am. Chem. Journ. 17 (1895), 607.
4) Wallach, Liebig's Annalen 245 (1888), 253; 252 (1889), 130.
5) Tilden, Journ. Chem. Soc N. S. 15 (1877), 554; 85 (1904), 759; Kremers, Pharm. Rundsch. (New York) 13 (1895), 135. Gildemeister and Kohler, Waliach-Festschrift, Gottingen 1909, p. 433.
Side by side with a-pinene, nopinene or B-pinene occurs in the turpentine oils, also in pine tar oil, in Siberian Fichtennadelol, and in the oils of lemon,1) coriander,2) cumin,3) hyssop4) and nutmeg. Presumably it will be found in a large number of volatile oils. Synthetically it has been prepared by Wallach.5) Starting with nopinone, this was condensed with bromacetic ester to nopinolacetic ester, which, when treated with acetic acid anhydride yielded ,i-pinene.
1) Gildemeister and Miiller, Wallach-Festschrift, Gottingen 1909, p. 442.
2) Walbaum and Muller, Ibidem 657; Report of Schimmel & Co. October 1909, 48.
3) Report of Schimmel & Co. October 1909, 50.
4) Gildemeister and Kohler, Wallach-Festschrift, Gottingen 1909, 417; Report of Schimmel & Co. April 1908, 58.
5) Liebig's Annalen 363 (1908), 1.
The following properties have been determined:
B. p. 164 to 166°; d15o 0,8650; aD - 19°29' (from hyssop oil); nD20o1,4754s.1)
In connection with two preparations obtained at different times, Wallach-) ascertained the following constants:
B. p. 163 to 164°; d22o 0,8675; aD - 22°5'; nD22o 1,4749.
B. p. 162 to 163°; d22o 0,8660; aD - 22°20'; nD22o 1,4724.2)
When acted on with glacial acetic acid-sulphuric acid mixture, B-pinene is in the main converted into terpinene.3)
(B-Pinene yields no nitrosochloride. With hydrogen chloride it yields a mixture of dipentene dihydrochloride and bornylchloride. When acted upon by nitrous acid, nitroso-/i-pinene results, which upon reduction is converted into amidoterebentene. This, in turn, when acted upon by nitrous acid, yields an alcohol, which when oxidized with chromic acid is converted into tetrahydrocuminic aldehyde (m. p. of the semicarbazone 201 to 203°) and cuminic acid (m. p. 1150).4) From a-pinene it is readily distinguished by means of its oxidation products. When oxidized with permanganate, there results nopinic acid (m. p. 126 to 127°) which is readily isolated by its difficultly soluble sodium salt. As a by product there also results a glycol melting at 76 to 78°. For the identification of B-pinene, fraction 160 to 170° is oxidized according to Wallach's5) directions for the preparation of no-pinate of sodium. 300 g. of pinene are shaken, with the aid of a shaking machine, with a solution of 700 g. potassium permanganate in 9 1. water to which 150 g. of sodium hydroxide have been added. The reaction mixture becomes decidedly warm and the oxidation is completed in about 20 minutes. In the absence of alkali, about 12 hours are required before the permanganate is consumed. The excess of hydrocarbon is distilled off with steam, the mixture filtered to remove the oxide of manganese and the filtrate evaporated to about 3 1. while a current of carbon dioxide is passed into the evaporating liquid. Upon cooling, nopinate of sodium crystallizes out, which is separated with the aid of a forcefilter and purified by recrystallization.
1) Report of Schimmel & Co. April 1908, 58. 2) Liebig's Annalen 363 (1908), 1.
3) Wallach, Liebig's Annalen 363 (1908), 1.
4) Pesci and Bettelli, Gazz. chim. ital. 16 (1886), 337; Wallach, Liebig's Annalen 346 (1906), 246.
5) Wallach, Liebig's Annalen 356 (1907), 228.
The free nopinic acid from l-B-pinene has the following properties: m. p. 126°; d17o 0,781; [a]D - 15,64° (in ethereal solution).
For its further characterization nopinic acid can be oxidized to nopinone with either lead peroxide or permanganate in sulphuric acid solution. Nopinone is a ketone which has served as a steppingstone in the accomplishment of several interesting syntheses of terpenes and terpene derivatives. Of the derivatives of this ketone the following should be mentioned: the semi-carbazone, m. p. 188°; the benzylidene compound, m. p. 106 to 107°; and the compound C18H290C13 which results when HC1 is passed into the alcoholic solution of the ketone and which melts at 148°.